1. Field of the Invention
The present invention relates, in general, to a method for detecting wafer defects and, more particularly, to formation of dummy dies at edge portions of a flat wafer which are utilized as an alignment mark such that the data for wafer defects can be maintained at further processes.
2. Description of the Prior Art
A semiconductor device is obtained by carrying out many process steps on a wafer. The reliability and yield of the semiconductor device can be improved by detecting various defects which may be generated in each step with a defect detecting apparatus and analyzing the causes of the defects rapidly and smoothly.
From an early step of a fabrication method of a semiconductor device, responsible for a flat wafer such as a better wafer, a well-formed wafer or a film-deposited wafer, until a step just prior to forming an element isolation film, no alignment mark is formed on the wafer.
When the flat wafer having no alignment mark is inspected for defects by a detecting apparatus, the sizes and coordinates (x, y) of defects in the flat wafer are determined. However, when reviewing the wafer defects after the wafer has been withdrawn from the apparatus, the pre-determined coordinates cannot be found because the wafer has been inspected for the defects in the absence of an alignment mark, a reference of the wafer. That is, it is anticipated that the wafer devoid of an alignment mark plays no role in utilizing the data for defects. This is attributed to the fact that, although there is information for the coordinates and sizes of defects which are detected before the element-isolating step, the absence of reference coordinates in the wafer cannot allow the detected coordinates and sizes to be correctly connected with the data for defects which are inspected with a reference of a certain point within a pattern before the element-isolating step. Accordingly, researchers always find great difficulty in defect analysis because they cannot know which steps the defects are generated at or how the defects progress.